After a decade in the South Australian Parliament from 1997, Senator Xenophon moved across to federal politics in 2007.

He said he did that because he believed he could do more for his state as an independent in Canberra.

He said since South Australia's massive power blackout last year and record power prices, he concluded the state's problems could not be fixed in Canberra without first fixing what he called a "broken political system back home".

Who will replace Nick Xenophon in the Senate?

If Nick Xenophon is disqualified based on his citizenship, there will be a recount and Tim Storer will be elected.

If he is not disqualified, when he resigns, his party can nominate the replacement.

Either way, there will be another Nick Xenophon person in the Upper House.

It will actually give more face to the other three members of the party that are currently there.

Nick does nominate them. In the seat of Hartley that he is running for in SA, 2.4 is the margin.

The election of Hartley always seems to be held by Italian speakers. It is where the Italian community heavily settled in Adelaide. He has lived there and it makes him competitive.

It is currently held by the Liberal Party by Vincent Tavzia.

NXT haven't stood in the lower house in SA before. That will be the big difference. It makes the contest for Government very different.

Analysis by ABC election analyst Antony Green

Senator Xenophon will remain in the Senate until the High Court determines his citizenship status.

"I will remain in the Senate fighting for the state, until the High Court determines the outcome of the so-called citizenship case affecting me and six others," he said.

"While my lawyers are confident I will succeed, whatever the outcome, once that decision is handed down I will be in a position to leave the Senate."

He will then contest the South Australian seat of Hartley, centred around Adelaide's inner north-eastern suburbs.

"Running for the seat of Hartley will be a big gamble for me, even though, as you know, I'm not a gambler," Senator Xenophon said.

"I'm sure that both Labor and the Liberals will pull out all the stops to try to prevent me and my team from breaking through into State Parliament.

"Just keeping the lights on over the next summer will be presented by the Government as a major achievement to be lauded and applauded. It's embarrassing," he said.

"Our state politics is broken, politically bankrupt ... We have the same old soap opera script between Labor and Liberal, but little real policy debate, let alone solutions for the state's many troubles.

"To quote Shakespeare, it seems our State Parliament has become nothing more than a stage for a troupe of players, led by the Premier and the Opposition Leader.

"Nick Xenophon has made a valued contribution to the Senate throughout his federal career. We have worked well together fighting for local jobs and protecting the Murray, and while he and I were not on the same side on all issues, we share a passion for South Australia."